In an axial-flow machine such as a gas turbine engine or the like having a blade row, inner and outer radial walls surround a flow path and a boundary layer grows on the wall. In the boundary layer on the wall, a secondary flow having a different velocity component from a main flow is generated due to, for example, pressure gradient between the blades. It is known that the secondary flow causes a pressure loss (energy loss).
As one means for reducing the secondary flow loss, there is an art in which a slope is provided on the radial wall facing the flow path to moderate the pressure gradient between the blades, as disclosed in U.S. Pat. No. 6,283,713.